A cat may look at a king is an English proverb that means even someone of low status has rights.
It is found first in print in a famous early collection of English proverbs, The Proverbs And Epigrams Of John Heywood, 1562.
In 1713, Oswald Dykes published English proverbs with moral reflexions. This used various well-known proverbs as a starting point for Dykes' to pronounce his political and social values. In this extract it isn't clear which king he was protecting, as Queen Anne was the British monarch at the time.
It was also used by Lewis Carroll in Alice's Adventures in Wonderland. Chapter 8. The Queen's Croquet-Ground"